Certain conventional encoders are connected to an external control circuit, etc., via a connector for deriving output signals or inputting/outputting control signals. For a structure of such a connector, for example, reference is made to FIGS. 4 and 5. The structure illustrated in FIG. 4 has a connector 4 coupled to the posterior part of encoder cover 2 mounted on an encoder body 1. That is to say, the connector is coupled to the encoder cover from the upper side. Connector 4 is coupled to cover 2 through gasket 42 for maintaining air tightness inside of the body. The geometry of cover 2 is generally adapted to match the geometry of the encoder body, for example, a cylindrical shape with one end closed, a squarish box shape, etc.
Encoder body 1 has components for detecting the number of revolutions or the rotation angle of a rotating element, such as a servomotor. Specifically, the body 1 has rotation axis 1b placed at part 1a of body 1. A coding plate is attached to this rotation axis 1b, in which a light transmitting area and a light shielding area are formed in a predetermined pattern. A light source is provided for irradiating light to the pattern-forming parts of this coding plate. A light sensor receiving light transmitted through the coding plate is arranged opposite of the light source with the coding plate arranged therebetween. An electronic circuit is provided for outputting an electric signal corresponding to the rotation angle. The rotation axis 1b is attached to the rotation axis of the rotating element to be measured, e.g., by a conventional device, and, then, the rotation action of the rotating element will be transmitted to the rotation axis 1b. 
In the structure illustrated in FIG. 5, connector 4 is attached to the side part of encoder cover 2. That is to say, in this structure, the connector is coupled from the side. The arrangement of the rest of the components of the structure is similar to that illustrated in FIG. 4.
An encoder outputting the output signals of the encoder via a connector directly fixed on an electric member is described, for example, in Japanese Published Patent Application No. 9-243409. Furthermore, an encoder in which a connector is integrated with a cover is described, for example, in Japanese Published Patent Application No. 2002-151192.
In this manner, the direction to connect the connector from the rear part as illustrated in FIG. 4, from the side part as illustrated in FIG. 5, or from another direction such as diagonally, backward, etc., depends on an apparatus to which the connector is coupled or a customer's specifications. Therefore, since a number of covers 2 may need to be provided for each type of encoder to correspond to the apparatus to which the encoder to be attached or the customer's specification, cost reduction in this technology is not believed to have been sufficiently achieved. Moreover, even if the specification of an encoder body is matched, the cover may have to be redesigned, which may lead to a considerable delay of delivery or possible loss of the customer. Such a problem may more pronounced, e.g., with recent rapid development in apparatus technology and control devices.